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Les Arcs, March 16-23 2002

The XXXVII th Rencontres de Moriond QCD AND HIGH ENERGY HADRONIC INTERACTIONS. Oscillations. B. s. Les Arcs, March 16-23 2002. Results from CDF, SLD and the LEP experiments New ALEPH results for these Winter Conferences Combinations from BOSC working group (many thanks to O. Schneider)

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Les Arcs, March 16-23 2002

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  1. The XXXVIIth Rencontres de Moriond QCD AND HIGH ENERGY HADRONIC INTERACTIONS Oscillations B s Les Arcs, March 16-23 2002 Results from CDF, SLD and the LEP experiments New ALEPH results for these Winter Conferences Combinations from BOSC working group (many thanks to O. Schneider) Conclusions CERN-EP/2002-016 Submitted to EPJ D.Abbaneo

  2. Example: (LEP-like numbers) sp/p = 0.15 sL= 250 mm p = 32 GeV/c Signal only No mistag Phenomenology Time-dependent asymmetry between “mixed” and “unmixed” decays Oscillating term damped by the exponential decay and proper time resolution effects st = (m/p) sL (sp/p) t D.Abbaneo

  3. Initial state Final state IP S.V. Bs candidate K Kf Opposite hemisphere P.V. charge, S.V. charge, Jet charges, Kaon charge, Lepton charge & kinematics Same hemisphere P.V. charge, Kf charge Overall F-B asymmetry (very effective @ SLD!) h  25% @ LEP h  15% @ SLD The basic strategy • Choose a selection criterion • determines directly the final state tag method • and signal fraction • Tag initial and final state • total mistag h = hi ( 1-hf ) + hf ( 1-hi ) • Measure proper time resolution: st = (m/p) sL (sp/p) t • Maximum likelihood fit toDms (or to the oscillation amplitude with fixed frequency) D.Abbaneo

  4. Selection methods Statistics • Fully inclusiveDelphi, SLD • FS tag from dipole or NN • Very high statistics ( N  105 @ LEP, N  104 @ SLD ) • “Natural” signal purity ( fs = 10%) • Semi-inclusiveAleph, Delphi, Opal, CDF, SLD • Inclusive l, f-l, K • Still high statistics ( N  104105 @ LEP, N  103 @ SLD ) • Signal purity “natural” or slightly enhanced. • Semi-exclusiveAleph, Delphi, Opal, SLD • Ds-h, Ds-l • Lower statistics ( N  102103 @ LEP, N  102 @ SLD ) • Signal purity up to 60%, controlled from data. • Fully exclusiveAleph, Delphi • Little statistics ( N  50 events ) • Purity  50%, excellent proper time resolution! Signal purity Resolution D.Abbaneo

  5. Key point sL, sp Crucial for inclusive analyses Resolution, bias corrections and pull corrections vary WIDELY as a function of the event topology. Careful event-by-event treatment is essential especially for the vertexing. Thestatisticalpowerathighfrequencydependscruciallyon acarefuldescriptionof the sample. The oscillation fit For every event: sL, sp, fj, Pjestimated event-by-event Each event is treated as a single experiment! D.Abbaneo

  6. P(t) = ½ Ge-Gt [ 1  cos(Dmst) ] P(t) = ½ Ge-Gt [ 1 Acos(wt) ] Fit for theamplitudeof an oscillation with agiven frequency* All w values for which A + 1.645 sA < 1 are excluded at 95% C.L. The amplitude method Set a limit by combining analyses unable to resolve oscillations: A=0 for Dms » w A=1 for Dms = w sA-1 (w)  N½ fs (1-2h) F (sp,sL) F (sp,sL)  exp(-st w ) For w Dms, the shape A (w) depends on the details of the analysis, and can be calculated analytically** in simple cases * Moser and Roussarie NIM A 384 (1997) 491 ** Abbaneo and Boix JHEP 08 (1999) 004 D.Abbaneo

  7. l+ Initial state Final state B 0 s IP n S.V. Bs candidate K Ds- Kf l+ B 0 s n “topological” c meson p+ B 0 s Ds- The three ALEPH analyses Released as preliminary in 2000 - now improved and submitted for publication Inclusive lepton final states Fully reconstructed candidates Ds - lepton final states Old Ds – hadron analysis dropped D.Abbaneo

  8. B+ control sample g, p0 recovery All Fully reconstructed candidates 80 candidates(32 in the main peak) 11 with purity > 80% 23 with purity > 50% D.Abbaneo

  9. (D -l) candidates: the channels s D+K+K-p+ Fraction of the resonant component estimated from the data NN to discriminate resonant background Over 300 candidates D.Abbaneo

  10. lepton charm Basic idea: Reconstruct inclusively a “D track” and fit it with the lepton Define a “B track” passing through the PV, with angular uncertainties parameterized from the simulation charm photon Look for photons around the D track with m(D,g)<1.8 GeV Improve the D direction Fit the D track, the B track and the lepton to find the B decay vertex lepton charm Decay length for the inclusive l analysis D.Abbaneo

  11. Initial state tag Final state tag Event-by-event treatment for the incl l analysis Divide events in classes according to topological properties [vertex classes] m(D), cosq(l,D), ntr(D), c2(D), c2(B) For each class: D.Abbaneo

  12. Sample composition Parameterized as a function of event properties Event-by-event treatment for the incl l analysis Decay length uncertainty from the vertex fit [data] Decay length bias correction and pull correction Momentum uncertainty and bias correction D.Abbaneo

  13. Simulated hadronic events (1.6 x data stat) Sample of Bs events in simulated hadronic events • Control reliability of simulation Use control samples to check IS tag, decay length and momentum reconstruction Building a reliable analysis • Control reliability of parameterizations [MC] D.Abbaneo

  14. The estimate of the systematic uncertainties For each source considered, both a change of the amplitude and of its statistical error are observed Calculate the total error taking into account both effects by means of toy experiments D.Abbaneo

  15. The three analysis results Inclusive lepton Ds-lepton Exclusive Obs. limit: ms>2.4 ps-1 Exp. limit: ms>0.3 ps-1 ms>7.2 ps-1 ms>7.4 ps-1(was 6.6 ps-1) ms>11.4 ps-1(was 9.5 ps-1) ms>14.0 ps-1(was 9.8 ps-1) 1.645A@15ps-1: 2.5 1.645A@15ps-1: 1.2 1.645A@15ps-1: 2.1 D.Abbaneo

  16. “topological” b vertex Good at SLD Hard at LEP IP   “topological” c vertex Kf dq = |QD- QB||VD-VB|   Final state tag based on charge flow between b and cvertices Needs excellent vertexing capability! @ SLD: sL = 72 mm (60%) & 265 mm sp/p = 0.07 (60%) & 0.21 N = 8.5K decays (4  inclusive lepton) B D B D - s + s 0 s 0 s Charge dipole Fully inclusive final states D.Abbaneo

  17. SLD versus LEP SLD privileged environment for Bs oscillation hunt LEP SLD 4M qq events <400K qq events per experiment sL 250 mm (core) sL 60-70 mm (core) Initial State Tag Initial State Tag heff 25% heff 10-15% (beam polarization) Best analyses: Best analyses: Ds lepton Inclusive lepton Inclusive lepton Fully inclusive D.Abbaneo

  18. Amplitude error reduction Now Summer99 @ 10 ps-1 0.220.33 @ 15 ps-1 0.390.66 @ 20 ps-1 0.641.27 The world combination Combined limit Dms > 14.9 ps-1 @ 95% CL Expected limit Dms = 19.3 ps-1 D.Abbaneo

  19. Comparison by experiment Weights in the combination Sensitivities D.Abbaneo

  20. Conclusions Bs oscillation searches have substantially improved over the last two years in the absence of new data! (e.g. the uncertainty at w  20 ps-1 was reduced by a factor  2) Some improvements can still be expected, but not as significant We know that Dms > 14.9 ps-1 @ 95% CL and we have a (mild) indication of a signal at w between 16 and 20 ps-1 The burden and the pleasure of continuing the hunt goes now to CDF and D0 D.Abbaneo

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